1. Field of the Invention
The present invention relates to a gas spectrometer. In particular, the invention relates to a method and apparatus for exciting a plasma in a gas for use in the gas spectrometer.
2. Description of Related Art
Detection and monitoring of gases are of great importance in many applications. For example, often a laboratory instrument to measure gases is required. Harmful fumes can be emitted from industrial site containers (e.g., plating and etching baths). Dangerous gases may be emitted in mines, or anaesthesia gases may fill a surgical operating room. To detect such gases and monitor their concentration, known spectrometers employ an instrument that uses the physical phenomenon known as Raman scattering. Such instruments have a laser that directs an intense beam through a chamber containing a sample of the gas to be measured. The sample gas produces a weak stimulated emission that is frequency (i.e., wavelength) shifted from the original stimulating laser beam. The magnitude of this frequency shift is dependent on the sample gas type.
There are several patents that describe improvements to the methods of measuring Raman scattering. U.S. Pat. No. 5,929,981 to Keilback describes a system for monitoring contamination of optical elements in a Raman gas analyzer. U.S. Pat. No. 5,673,109 to Keilback describes a system and method for increasing the efficiency of a Raman gas analysis system. U.S. Pat. No. 5,521,703 to Mitchell describes a diode laser pumped Raman gas analysis system with reflective hollow tube gas cell. U.S. Pat. No. 5,506,678 to Carlsen et al. describes a system for collecting weakly scattered electromagnetic radiation for a Raman gas analysis system.
Known gas chromatographic analyzers pass a gas mixture down a column where individual gases in the gas mixture adsorb and release from the column walls at different rates. The temperature at which the column walls are maintained will often alter the rate at which particular gases adsorb to the walls. U.S. Pat. No. 6,093,921 to Gaisford et al. describes a microwave heating apparatus for gas chromatographic columns to achieve a controlled temperature profile along the length of the column.
In the background to U.S. Pat. No. 4,654,504 to Sullivan, et al., there is described a detector in which a gas containing chemical compounds to be analyzed is passed through a tube mounted within a resonant cavity that is powered by magnetron of the type used in a microwave oven for the home. U.S. Pat. No. 4,654,504 to Sullivan, et al., incorporated herein by reference, goes on to describe the cooling of the discharge tube by flowing a coolant into thermal communication with an outside surface of the discharge tube so as to reduce the erosion of the inner surface of the discharge tube and attain a satisfactory discharge tube life.
However, known analysis systems that analyze the gases out of such gas chromatographic systems do not have a solid-state signal power source that sustains the gas in a plasma state for the analysis of the spectra of the light emitted from the plasma.
It is an object to the present invention to provide an emission source with a long life discharge tube. It is another object of this invention to provide a solid state power source for a signal that sustains a plasma in an emission source. It is a further object of the present invention to provide an emission source within a discharge tube sustained by a low cost simple solid-state signal power source.
These and other objects are achieved in a gas plasma emission source that includes a solid state signal power source coupled to a resonant cavity.
Alternatively, these and other objects are achieved in an atomic emission detector that includes a solid state signal power source coupled to a resonant cavity and a spectrographic detector to sense atomic emissions from a gas within the resonant cavity.
In another alternative embodiment, these and other objects are achieved with a method of sustaining a plasma that includes passing a gas through a resonant cavity and exciting the resonant cavity with signal power from a solid state power source to sustain the plasma in the gas.
In yet another embodiment of the invention, these and other objects are achieved with a method of using a solid state power source that includes passing a gas through a resonant cavity and coupling sufficient signal power from an output of the solid state power source to sustain a plasma in the gas where the sufficient power is less than 300 watts.